nie | The American Naturalist. [September, 
BOTANY. 
Yucca Pollination.—Probably the most interesting case of insect 
pollination known is that of Yucca by the little moth Pronuba. 
Under the title, “ Yucca Moth and Yucca Pollination,” Dr. C. V. 
Riley has lately summarized the results of observations and investiga- 
tions on this interesting subject. Having myself verified many of the 
observations detailed, I have consented, at Dr. Bessey’s request, to out- 
line the process of pollination as at present understood, for the Nart- 
URALIST. 
Dr. Geo. Englemann’ was evidently the first observer to notice the 
Yucca moth and suspect its relation to the pollination of Yucca. 
Specimens of the moth were sent to Dr. Riley who christened it 
Pronuba yuccasella’, and took up the investigation of the subject 
obtaining surprising results. The subject has since been much studied 
but to Drs. Riley and Trelease we are chiefly indebted for its develop- 
ment. 
Self fertilization in Yucca is practically impossible. The stamens 
curve away from the pistil, in several cases very strongly, thus placing 
the pollen at some distance from the pistil. The pollen furthermore 
is glutinous and not easily detached and blown about; and the three 
lobes of the stigma are erect and so arranged that pollen dropping 
cannot fall into the stigmatic tube into which, it is further found, the 
pollen must be inserted some distance to be effective. Thus Yycea is 
entirely dependent on outside aid for pollination. Few species of plants, 
if any, depend upon one species of insect for pollination. Many have 
very numerous pollinators. Yuccas, however, appear to be actually 
dependent upon some one species of the little moth Pronuba. All 
species of Yucca east of the Rocky Mountains are spea 
dependent upon Pronuba yuccasella. 
IThird Annual Report Missouri Botanical Garden, 1892, pp. 99-158, 10 platen 
The reader is referred to this article for all details. The life history of Pronuġa and 
Prodoxus tN bogus Yucca moth) is discussed, and SEREGE of all known species 
ded. Several species are describe 
‘ The Flower of Yucca and its POER ” Bull. Torr. Bot. Club, vol. iii, no. 7 
A 1872), and “ Notes on the Genus Yucca,” Trans. Acad. Sci. of St. Louis, vol. 
iii, No. 1 (Apil, 1878). 
5 On a new Genus in the Lepidopterous Family Tineide, with Remarks on the 
Feriilisatióa of Yucca,” Trans, Acad. Sci. of St. Louis, vol. iii, No. 1, p. 55 (April, 
18 
